Hermetic seal for light-sensitive material



Dec. 20, 1938. c s TREACY 2,140,725

' HERMETIC SEAL FOR LIGHT-SENSITIVE MATERIAL Filed April 16, 1935 I2) I a I l 'I I l I I/-I0 I I I I I I IO' J/ H g I I I I L T J INVENTOR Lf Egril 5. TIEHE ATTORNEY Patented Dec. 20, 1938 PATENT OFFICE HERMETIC SEAL FOR LIGHT-SENSITIVE MATERIAL Cyril S. Trcacy,

United Research Corporation, Long Scarsdale, N. Y., assignor to Island City, N. Y., a corporation of Delaware Application April 16, 1935, Serial No. 16,578

4 Claims.

This invention relates to a light sensitive cell and the method of constructing the same, and is in the nature of an improvement of an element of the cell construction shown in an application of Carpenter and Ross, Serial No. 747,610 filed October 9, 1934, which has matured into Patent No. 2,041,816, in which the complete assembly is disclosed and claimed.

An object of the present invention is to prolll vide a more emcient hermetic seal for the protection of the selenium used in a light sensitive cell. Selenium being subject to variations in moisture, it becomes important to hermetically seal the active portion of the cell in an operative position 15 and still retain its relative proportions as disclosed in the above-mentioned application.

The manner in which this is accomplished will be apparent from the following description and accompanying drawing wherein:

2Q l is a perspective view of a light sensitive cell assembly.

Fig. 2 is a plan section taken in a plane along line 2Z2 of Fig. 1.

Fig. 3 is a sectional elevation taken in a plane 25 along line 53-43 of Fig. 2; and

Fig. i is an enlarged detail view taken along the line 4- 3 of Fig. 3 and showing the interdigitated electrodes.

Referring now to the details of the drawing in which like numerals indicate like elements, a light sensitive cell i has a base member 2, which is preferably formed of porcelain, isolantite, Bakelite, or other suitable insulating material. A recess 3 is provided in one side of the base 2 35 to receive an electrode assembly generally indicated at 4. The assembly l includes a transparent base plate 5, such as glass, on the rear side of which is plated or fused a coating of hard metal 6, generally an alloy of platinum or pal- 4,0 ladium, for example, as disclosed in the patent to Carpenter, No. 1,940,245. Over the metal 6 another coating 1 and l of a softer metal such as silver is placed, as shown in Fig. 3, to provide a base on which wires 8 and 8 may be soldered.

After the layer 6 has been deposited on the surface of the glass plate 5, it is separated into two sections or electrodes Ill and ill by tracing a sinuous path l l thereon to form a series of intero digitated projections 12 and [3 as will be seen in Fig. 4. A thin layer of selenium M or other light sensitive material is then deposited on the face of the metal 6 to bridge the gap formed between the two electrodes I 0 and I0. This is usually accomplished by sublimation, that is, by vaporizing the light sensitive material from a solid and allowing it to condense upon the metal 6.

To protect the selenium surface a cup-shaped piece of glass [5 is placed thereover at the rear surface of the metal layerG. This glass cap is 5 sealed to the metal surface by a cementing wax l8. In this particular feature my cell construction differs from that referred to in the aboveidentified application and is an improvement thereover from the standpoint of structural design which provides an improved seal. It is very desirable to produce under the glass cap a partial vacuum and this is accomplished by heating the glass member 5 and the cap to a temperature above the melting point of the wax, and as the 16 cap is held tightly upon the metal surface, the wax is applied at the contact edge between the surface and cap and fills the recess groove ll so provided. When this assembly cools a partial vacuum is created under the glass cap and around 20 the selenium and there is therefore a certain pressure produced on the cementing material.

To prevent the sealing material, which is melted to a liquid when applied to the cap, from entering the chamber and thus covering a portion of the active surface, the cap is provided with a single ring contact surface which may be more firmly fitted to the surface than a doubleridged cap or a cap having its contact edge of the same width as its body portion. The large groove formed by narrowing the contact edge also permits sufflcient wax to be applied at the optimum position to provide a particularly efficient seal between the cap and the metal surface. This type of cap prevents the cement from seeping under the glass and therefore provides a. hermetic seal. To further protect the selenium from moisture, I apply a coating of moisture-proof material l9, such as asphalt, to the electrode assembly 4.

A recess 2| is formed in the base 2 to allow the cup member l5 to 'be received therein. Also, a pair of vertically disposed grooves 22 and 23 are formed in the top and bottom of the base member 2 to receive the wires 8 and 9. The upper and lower portions of the outer surface of the base 2 are also recessed as at 24 and 25 to receive metal caps 26 and 2'! which have soldered thereto the wires 8 and 9, as shown at 28 and 29, respectively. It will be seen, therefore, that the caps 26 and 21 serve to form contact terminals for the electrodes 60 I0 and I0 as well as to form retainers to hold the assembly in place.

In order to hold the caps 26 and 21 in position,

I provide detents; (not shown) in the base 2 wherein the sides of the caps are indented as at and 3| in Fig. 1.

The cell may be assembled as follows: The leadin wires 8 and 9 are soldered to their respective electrodes I 0 and I 0', the wires 8 and 9 at this time being substantially longer than as shown in Fig. 3. The electrode assembly I is then placed in the recess 3 and the caps 28 and 21 are fitted into the position shown in Fig. 3, after threading the wires 8 and 9 through the apertures 28' and 29' in the caps 25 and 27 respectively. The caps are then fastened in position by indenting the same at 30 and 3| in Fig. 1 into indentations, not shown, in the base 2, similar indentations, not shown, also being provided in the opposite side of the cell. The wires 8 and 9 are now pulled to bring the electrode assembly 4 in contact with the bottom of the recess 3, as shown in Fig. 3, and the wires 8 and 9 are soldered to the caps 26 and 21, respectively, as shown at 28 and 29, and the surplus portion of these wires 8 and 9 which extends beyond the caps is removed.

Having thus described my invention, what is claimed as new and desired to secure by Letters Patent is:

1. In a light sensitive cell construction, a base plate having a flat surface, interdigitated electrodes on said surface, light sensitive material bridging said electrodes, a hollow cap covering said material, said cap contacting said surface and having a single inner contact edge of smaller thickness than the body of said cap, and cementing material at the contact of said cap and said base plate and underlying the body of said cap.

2. A light sensitive cell cover for light sensitive material deposited on a substantially flat siu'i'ace comprising a hollow cover can positioned over said material, said cap contacting said surface and having a single narrower contact portion than body portion with a groove on the external diameter thereof, and a cementing material filling said groove and underlying said body portion.

3. A light sensitive cell construction comprising a transparent plate having a flat surface, electrodes on said flat surface, light sensitive material bridging said electrodes, a hollow cap positioned over and contacting said light sensitive material,

said cap having a wall with a single contact edge of lesser width and diameter than the body of the wall of said cap, cementing material positioned in the groove formed by said edge of lesser width, and underlying the major portion of the wall of the body of said cap, and a moistureproof material covering said cap and said cementing material.

4. The method of providing a partial vacuum for the active portion of a light sensitive material deposited on a flat surface within a grooved hollow cap, comprising heating said surface and said cap to a predetermined temperature above the operating temperature of said surface, and hermetically sealing said active portion of said light sensitive material within the chamber by applying at the contact edge between said surface and said cap, with said cap in position, a cementing material which is a solid at the operating temperature of said light sensitive material the partial vacuum being created upon the cooling of said materials.

CYRIL S. TREACY. 

